Full-scene anti-aliasing method and system

ABSTRACT

A method and system for performing full-scene anti-aliasing for an image through a technique of rotating and unrotating rasterization of a scene and rendering a resulting image. A scene is rasterized at a first angle relative to a first coordinate system to generate a plurality of pixels, which are then applied to a polygon surface that is rendered at a second angle equal to the inverse of the first angle. Thus, the resulting image is re-oriented with respect to the first coordinate system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/079,840, filed on Mar. 27, 2008, which is a continuation of U.S.patent application Ser. No. 11/477,326, filed on Jun. 28, 2006, whichissued as U.S. Pat. No. 7,369,138 on May 6, 2008, which is a divisionalof U.S. patent application Ser. No. 10/837,234, filed on Apr. 30, 2004,which issued as U.S. Pat. No. 7,119,812 on Oct. 10, 2006, which is adivisional of U.S. patent application Ser. No. 10/233,106, filed on Aug.28, 2002, which issued as U.S. Pat. No. 6,922,199 on Jul. 26, 2005, allof which are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention is related generally to the field of sampledimagery, and more particularly, a system and method for generatinganti-aliased sampled images and sampling images by computation oracquisition while reducing aliasing.

BACKGROUND OF THE INVENTION

In computer graphics, input geometry or the like is typically used torepresent a scene from which a sampled image is created. A sampled imageis a grid, or “raster,” of discrete samples referred to as pixels. Thepixels are generally arranged along two perpendicular axes correspondingto the horizontal and vertical axes of the image. Rendering a scene isthe process of creating such an image of the scene. This process is alsocalled rasterization. The value of a pixel is determined by calculatinga sample value from the scene. The rasterized image, represented by thegrid of pixels, is typically displayed visually, such as being printedor displayed upon a computer display monitor. The number of pixels andnumber of colors or values used in rendering a graphics image limit, tosome extent, the quality, accuracy, and various characteristics of theimage displayed, (for example, the image sampling accuracy, smoothness,detail, and resolution). A great amount of effort has been devoted todeveloping sophisticated graphics processing, rendering, and samplingmethods for improving image quality. Rendering sampled images, however,produces unwanted artifacts. This production is called “aliasing.” An“anti-aliased” rendering method aims to reduce objectionable artifacts.

In addition to higher quality static images, rendering high-qualityanimation depicting visual effects of motion is also desirable. Theillusion of motion is created by quickly displaying related images in asequence in which an object changes appearance slightly. Although theanimation of the object may appear to be continuous, each frame of thesequence is a separate image that is displayed momentarily. Thus, thequality of each frame impacts the quality of the overall animation orillusion of motion. Depending upon the method by which the sequence ofimages is sampled, the resulting representation of motion may result inthe creation of motion artifacts. The more noticeable effects include“crawling” and “popping” of pixels on an edge of an object having acolor that contrasts sharply with a different colored background.

For example, consider an object of a first color having a straight edge,that appears to be moving across a background of a second color. As theedge of the object moves across the boundary of a pixel, at some pointthere must be a determination as to how and when the color of the pixelchanges from the color of the background to the color of the object. Ifthe value of the pixel is taken from a single sample point, then whenthe edge of the object passes the sample point of the pixel, the colorof the pixel is changed. The location of a single sample point istypically in the center of the pixel, and consequently, the color of apixel is determined by the color at the center of the pixel. As a resultthe edge of the object may be well within the region defined by thepixel, but the pixel may still have the color of the background becausethe edge has not reached the center (i.e., the sample point) of thepixel.

When multiple frames of images are displayed in sequence to provide theillusion of an object in motion, the effect of pixels along the edge ofthe object “popping” from one color or value to another can bedistracting for a viewer. The relative motion of an object with respectto the orientation of the sampling grid of the image may be such thatpixels along the edge of the object pop values in a manner and with aregularity that create a visual crawling effect along the edge of theobject.

There have been many different approaches to addressing the issue ofsuch aliasing artifacts, including motion artifacts and “staircasing.”One such approach is to increase the resolution, or the number of pixelsused to represent an image. For example, the available resolution ofcomputer graphics has increased dramatically since the first monochromecomputer monitors were developed, and undoubtedly will continue to doso. Similarly, printing devices have ever increasing resolution as well.However, there are practical limitations on the manufacturing ofdisplays and other devices used for recreating an image. Computationallimitations must also be considered because there are practicallimitations with respect to the amount of data that can be processed inrendering an image. Moreover, no matter how high a resolution is used torepresent a graphics image, the image is still nevertheless sampled atdiscrete intervals, and consequently, subject to some degree ofaliasing, including motion artifacts.

Another approach has been to increase the number of values computed foreach pixel. More specifically in constructing an image, multi-samplinganti-aliasing systems might use sample values from multiple samplestaken at different locations within a pixel in determining the finalvalue of a pixel. As a result, as the edge of a moving object firstpasses over one of a pixel's sample points, the pixel may take on adifferent value that is a compromise between the value of the object andthat of the disparate background. For example, the pixel might changeits value each time the object covers another sample point of the pixel,until all of the sample points share the color of the object, the pixelfinally taking on the color of the object, assuming the size, shape, andmotion of the object's result in the object gradually and completelycovering the pixel.

The multiple samples for each pixel are typically arranged in an orderedpattern, such as in a rectangular grid where the sides of a rectangledefined by the positioned samples are parallel to the axes of thepixels. Previous approaches have also positioned the samples in a(pseudo)-random fashion. Random multi-sampling per pixel generallyrequires a considerable amount of computational power. As a result, someanti-aliasing algorithms employ sampling patterns which attempt tosimulate a random sampling pattern. However, these patterns may requirenearly the same computing power as for random multiple sampling perpixel.

Although conventional, multi-sample, full-scene anti-aliasing methodsgenerally do reduce motion artifacts and edge effects, in somesituations motion artifacts remain. Full-scene anti-aliasing isantialiased rendering of substantially a full frame. For example, whenan object has an edge parallel to an axis of the sampling pattern and ismoving in a direction perpendicular to the edge, a popping effect may becreated when the edge of the object passes through multiple samplepoints simultaneously. Taking more samples per pixel may reduce theseverity of multi-sampling motion artifacts, but processing overhead andeconomic considerations will place practical limits on the maximumnumber of samples that can be reasonably taken per pixel.

Therefore, there is a need for an alternative system and method forrendering an image from a representation of a scene, while reducingaliasing, such as motion artifacts and edge effects.

SUMMARY OF THE INVENTION

The present invention relates to a method and system for rendering atwo- or three-dimensional scene, producing a sampled image, whileminimizing aliasing. A scene is rasterized or sampled at a first anglerelative to a first coordinate system. The resultant raster, comprisinga plurality of pixels, is then rotated at a second angle equal to theinverse of the first angle. An image of the scene is then formed bysampling the pixels in the raster, producing an image that is properlyoriented with respect to the first coordinate system. The secondrotation may be performed by first applying the pixels to a polygonsurface. The pixels may be first converted to a texture map and appliedto the polygon surface as a texture. Then this polygon is rotated andrendered. The anti-aliasing technique may also include a super-samplingprocess, rasterizing the scene to produce a temporary surplus of pixels.To down-sample the number of pixels applied to the polygon surface,bilinear filtering may also be applied, when converting pixels to texelsto form a texture map to be applied to the polygon surface. Suchanti-aliased rendering may also be repeated on the scene, using two ormore different initial angles, rendering two or more separate imagesthat are ultimately combined, to produce a final resultant image. Theresult of multiple steps described above may be computed in a singlestep.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system in which embodiments of thepresent invention are implemented.

FIG. 2 is a block diagram of a graphics processing system in the systemof FIG. 1 according to an embodiment of the present invention.

FIG. 3 is a block diagram of a portion of a pixel engine according to anembodiment of the present invention in the graphics processing system ofFIG. 2.

FIG. 4 is a flow diagram of an anti-aliasing technique according to anembodiment of the present invention.

FIG. 5 is a flow diagram of an anti-aliasing technique according toanother embodiment of the present invention.

FIG. 6 is a flow diagram of an anti-aliasing technique according toanother embodiment of the present invention.

FIG. 7 is a flow diagram of an anti-aliasing technique according toanother embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention render anti-aliased images whilereducing artifacts in static images and/or in motion/animation. Thesystems and methods described herein rasterize a scene at an angle andapply the pixel values from the rasterization to a polygon rendered atthe inverse of the angle at which the scene was first rasterized.Embodiments of the invention may be called “rotate-unrotate” rendering.It will be appreciated that the terms “pixel,” “pixel value,” and“value” will be used herein interchangeably. When the terms are toconvey different meanings, it will be apparent from the context. Certaindetails are set forth below to provide a sufficient understanding of theinvention. However, it will be clear to one skilled in the art that theinvention may be practiced without these particular details. In otherinstances, well-known circuits, control signals, timing protocols, andsoftware operations have not been shown in detail in order to avoidunnecessarily obscuring the invention.

FIG. 1 illustrates a computer system 100 in which embodiments of thepresent invention are implemented. The computer system 100 includes aprocessor 104 coupled to a host memory 108 through a memory/businterface 112. The memory/bus interface 112 is coupled to an expansionbus 116, such as an industry standard architecture (ISA) bus or aperipheral component interconnect (PCI) bus. The computer system 100also includes one or more input devices 120, such as a keypad or amouse, coupled to the processor 104 through the expansion bus 116 andthe memory/bus interface 112. The input devices 120 allow an operator oran electronic device to input data to the computer system 100. One ormore output devices 124 are coupled to the processor 104 to provideoutput data generated by the processor 104. The output devices 124 arecoupled to the processor 104 through the expansion bus 116 andmemory/bus interface 112. Examples of output devices 124 include aprinter and a sound card driving audio speakers. One or more datastorage devices 128 are coupled to the processor 104 through thememory/bus interface 112 and the expansion bus 116 to store data in, orretrieve data from, storage media (not shown). Examples of storagedevices 128 and storage media include fixed disk drives, floppy diskdrives, tape cassettes and compact-disc read-only memory drives.

The computer system 100 further includes a graphics processing system132 coupled to the processor 104 and the host memory 108 through theexpansion bus 116 and memory/bus interface 112. Optionally, the graphicsprocessing system 132 may be coupled to the processor 104 and the hostmemory 108 through other types of architectures. For example, thegraphics processing system 132 may be coupled through the memory/businterface 112 and a high speed bus 136, such as an accelerated graphicsport (AGP), to provide the graphics processing system 132 with directmemory access (DMA) to the host memory 108. That is, the high speed bus136 and memory bus interface 112 allow the graphics processing system132 to read and write host memory 108 without the intervention of theprocessor 104. Thus, data may be transferred to, and from, the hostmemory 108 at transfer rates much greater than over the expansion bus116. A display 140 is coupled to the graphics processing system 132 todisplay graphics images. The display 140 may be any type of display,such as those commonly used for desktop computers, portable computers,and workstation or server applications, for example, a cathode ray tube(CRT), a field emission display (FED), a liquid crystal display (LCD),or the like.

FIG. 2 illustrates circuitry included within the graphics processingsystem 132, which performs various three-dimensional.(3D) graphicsfunctions. As shown in FIG. 2, a bus interface 200 couples the graphicsprocessing system 132 to the expansion bus 116. In the case where thegraphics processing system 132 is coupled to the processor 104 and thehost memory 108 through the high speed data bus 136 and the memory/businterface 112, the bus interface 200 will include a DMA controller (notshown) to coordinate transfer of data to and from the host memory 108and the processor 104. A graphics processor 204 is coupled to the businterface 200 and is designed to perform various graphics and videoprocessing functions, such as, but not limited to, generating vertexdata and performing vertex transformations for polygon graphicsprimitives that are used to model 3D objects. The graphics processor 204is coupled to a triangle engine 208 that includes circuitry forperforming various graphics functions, such as scissoring, attributetransformations, rendering of graphics primitives, and interpolation oftexture coordinates for a texture map.

A pixel engine 212 is coupled to receive the graphics data generated bythe triangle engine 208. The pixel engine 212 contains circuitry forperforming various graphics functions, such as, but not limited to,texture application or mapping, bilinear filtering, fog, blending, andcolor space conversion. The pixel engine further includes texture enginecircuitry 214. As will be described in more detail below, the textureengine circuitry 214 is employed in rendering a polygon surface rotatedat the inverse of the angle at which a scene was first rasterized.

A memory controller 216 coupled to the pixel engine 212 and the graphicsprocessor 204 handles memory requests to and from a local memory 220.The local memory 220 stores graphics data, such as source pixel valuesand destination pixel values. A display controller 224 is coupled to thememory controller 216 to receive processed destination values for pixelsthat are to be displayed. The output values from the display controller224 are subsequently provided to a display driver 232 that includescircuitry to provide digital color signals, or to convert digital colorsignals to red, green, and blue analog color signals, to drive thedisplay 140 (FIG. 1).

Although the texture engine circuitry 214 is illustrated as beingincluded within the pixel engine 212, it will be appreciated that thetexture engine circuitry 214 may also be a circuit separate from thepixel engine 212, or included in one of the aforementioned circuitblocks of the graphics processing system 132. Therefore, the particularlocation of the texture engine circuitry 214 is a detail that may bemodified without deviating from the subject matter of the invention andshould not be used in limiting the scope of the present invention.

A portion of a pixel processing pipeline 300 that may be used for thetexture engine circuitry 214 of the pixel engine 212 (FIG. 2) isillustrated in FIG. 3. A texture map buffer 302 stores texel data thatare provided to and applied by a texture application engine 304 tosurfaces defined by geometry data the texture application engine 304receives. Following application of a texture map to a surface, a texturerendering engine 306 calculates, from the texture-mapped surface, pixelvalues that will be used to represent an image. A blending unit 308 maybe included as part of the pixel processing pipeline 300 and is used forcombining or blending multiple pixel values for each pixel of an image.In this manner, the pixels of multiple images can be overlaid andproduce a resultant image where each pixel of the resultant image has avalue that is a combination of the multiple values of corresponding,overlying pixels. It may be appreciated that a texture may be “applied”to a surface, simply by defining the geometric relationship between adefined surface and a defined texture map. Operation of the textureengine circuitry 214 in embodiments of the present invention will beexplained in more detail below.

As mentioned previously, well-known circuits, control signals, timingprotocols, and software operations have not been shown in detail inorder to avoid unnecessarily obscuring the invention. However, it willbe appreciated that the texture map buffer 302, the texture applicationengine 304, the texture rendering engine 306, and the blending unit 308are conventional in design and operation, and the description providedherein is sufficient to enable those of ordinary skill in the art topractice the present invention. In summary, in embodiments of thepresent invention these elements may be used to render an image of ascene at a particular angle, as part of the operation of embodiments ofthe invention, or other elements may be used to render the image of agiven scene at a particular angle, in the operation of embodiments ofthe invention. Commonly, these elements are used to render scenes, andthese elements could be used to do so, at a selected angle. In theoperation of embodiments of the invention, in any case, whateveremployment of these elements in the rendering of the scene at aparticular angle, they or their analogues are then used to render animage rotated at the inverse angle, of the image rendered at the firstangle. It will be appreciated by those of ordinary skill in the art thatappropriate control circuits, data paths, and memory, etc. are employed,as necessary.

It will be further appreciated that the sample values calculated duringrasterization and applied to the polygon surface may represent valuessuch as color or grayscale at a sample location, and that the samplevalues for the samples may consist of several different components. Forexample, a sample value may represent colors which are the combinationof red, green, and blue color components. Another example includessample values representing colors which are the combination of luma andchroma components. Consequently, because it is well understood in theart, although circuitry to perform graphics operation for each of thecomponents is not expressly shown or described herein, embodiments ofthe present invention include circuitry, control signals, and the likenecessary to perform anti-aliased rendering of each component formulti-component sample values.

Embodiments of the present invention can use conventional renderingcircuitry/software to perform its operation. The operation of thegraphics processing system 132 will be described with respect to theflow diagram of FIG. 4. In operation, a scene is rasterized at an anglesuch that the pixel values that are stored into a back-buffer, withinlocal memory 220, for example, form an image rotated at an angle θ to afirst coordinate system. Typically, the first coordinate system is theworld space coordinate system where two axes are oriented along thehorizontal and vertical directions. Thus, when the rasterization occursat the angle θ, the image of the scene appears tilted. Were the valuesstored in the back-buffer to be displayed, the image would appear at anangle. So far, the texture engine may not have been used. However, inalternative embodiments of the present invention, the texture engine mayhave been used to render any texture-mapped polygons in the scene.

Possibly after format conversion and/or up sampling, the rasterizedpixel values are then treated as texel values of a texture map such thatthe rasterized scene is a texture that may be applied to the surface ofa polygon. The texture map is provided to the texture map buffer 302(FIG. 3) for storage. Geometry data is provided to the textureapplication engine 304 defining a polygon surface onto which theresulting texture stored in the texture map buffer 302 is applied.

The texture application engine 304 applies the texture map, representingthe rasterized scene at an angle θ, to the surface of the polygon, andthe texture rendering engine 306 renders the resulting polygon at anangle −θ. That is, the polygon is effectively rotated by the inverse ofthe initial rasterization angle to correctly reorient the image withrespect to the world space coordinates. The rendered polygon, which isnow oriented correctly, may be displayed in a conventional visualmedium, such as a computer display, a printer, or the like. Typically,the size of the polygon surface will be such that the display windowwill be filled by the interior of the polygon. However, it will beappreciated that the size, shape, and resolution of the polygon surfacemay be modified without departing from the scope of the presentinvention. Additionally, if the surface portion rendered is larger thanthe final image, the portion of the surface comprising the pixels neededto produce the final image will be extracted. The polygon onto which thetexture is applied may have any desired resolution, however, as will beexplained in more detail below, the desired resolution of the polygon istypically at least that of the desired output resolution.

It will be further appreciated that the angle θ can be selected invarious manners without departing from the scope of the presentinvention. For example, the angle θ can be preprogrammed to a certainvalue. Alternatively, the angle θ can be selected from a preselected setof angles. The selection may be made in an ordered fashion or in arandom or pseudo-random fashion as well. The preselected angles can be afixed set of angles or positions calculated in advance, so that choosingan angle from a group of preselected angles will mean that a table ofangles is constructed in advance, and then selections from the table aremade during anti-aliased rendering. However, it will be furtherappreciated that, as an alternative, angles or positions could begenerated in a constrained or controlled manner, to accomplish a similarresult. For example, angles could be generated randomly orpseudo-randomly, and then transformed such that a useful subset of thesebecome the set of preselected angles.

The anti-aliased rendering by embodiments of the present inventionreduce polygon popping and other aliasing which might result along thevertical and horizontal axis. When the scene is initially rasterized atthe angle θ, the sampling is oriented at an angle with respect to thedesired image and the pixels from the rasterization represent an imageof the rotated scene. Thus, horizontal and vertical lines in theoriginal scene are now de-emphasized rather than being accentuated bythe orientation of the scanlines. The scene is resampled during therendering of the polygon rotated at an inverse angle of the initialrasterization angle to reorient the image.

Another embodiment of the present invention is described in the flowdiagram of FIG. 5. The anti-aliasing algorithm illustrated in FIG. 5 issimilar to that illustrated in FIG. 4, however, rather than constructingthe texture map using point-sampling techniques, bilinear filtering isused in converting pixels into a texture map. It will be appreciated bythose of ordinary skill in the art, however, that in the embodimentdescribed with respect to FIG. 4, where rasterization is to desiredtexel locations, point-sampling is not necessary. In the embodimentshown in FIG. 5, as a result of bilinear filtering, artifacts that areintroduced when texels of the texture map do not fall on pixel centersare reduced, and the overall appearance of edges in the resultingtexture is smoothed further.

In a similar vein, illustrated in FIG. 6 is another embodiment of thepresent invention which relies on super-sampling during rasterization ofthe scene at an angle θ. The surplus of samples calculated during therasterization of the scene are subsequently down-sampled when renderingthe polygon surface. The combination of super-sampling and down-samplingenhances the subjective anti-aliasing quality, and can be efficientlyintegrated with the initial rasterization and the reorientingrasterization.

Although not shown in FIG. 6, the rotate-unrotate technique thatincludes super-sampling of a scene may be modified to further includedown-or up-sampling when converting the pixels to a texture map. Forexample, the number of pixels calculated through super-sampling canagain be doubled along each dimension of the resulting image to produceapproximately four times the number of texels for the texture map or, abilinear blending technique can be used during application to thesurface of the polygon to down-sample the number of texels to theappropriate output resolution.

Another embodiment of the present invention is shown in FIG. 7. Theanti-aliased rendering illustrated in FIG. 7 is similar to thatillustrated in FIG. 4; however, the scene is rasterized at two differentangles, θ₁ and θ₂, thus producing two frames of pixels that representimages of the scene, rotated, at the respective angles. Each of theframes of pixels is converted into, or treated as, a texture map ofrespective texels, which is subsequently applied to a respectivepolygon. Each polygon is then rendered as if rotated by the inverse ofthe respective initial rasterization angle. Both images now appear inthe same orientation. The resulting images are then aligned and combinedto produce a final image.

The values of the two respective rendered polygons can be combined in avariety of methods. For example, in one method of combining the valuesof the rendered polygons, the values of the first and second renderingsare averaged to provide values for the pixels of the resultant image.Thus, an aliasing artifact at one location in the first image may be dueto the angle in that the second image at the second angle may containless aliasing at that same location. The averaging minimizes the degreeof aliasing at such locations.

Another approach to combining the rendered images is to use analpha-blending technique, where the pixels of the rendered polygons areoverlaid and the respective opacity or alpha values are adjusted toyield composites for the pixels of the resultant image. In the casewhere the pixels are alpha-blended, the values of correspondinglylocated pixels are scaled by their respective alpha values, and then thescaled values are summed together to yield a resulting value for eachpixel. However, other alpha- or opacity-blending techniques may beapplied as well.

Still another method of combining the rendered images is to interlace ordisplay in an alternating sequence the rendered images. Videointerlacing can be used to effect a blending of multiple frame buffers.In conventional NTSC television, each interlaced video frame consists oftwo images called “fields.” Each field is the even or odd lines of theimage. When displaying video, the television updates each field every1/60^(th) of a second. If the pixels from one frame buffer are used asthe first field, while pixels from a different frame buffer are used forthe second field, the interlacing apparatus will construct an outputimage which is a combination of both input images. Another similartechnique for blending multiple frames involves displaying the unblendedframes at a rate sufficient for the human eye to fuse images together.

Combining pixels of n framebuffers: the values are combined by summingthe respective values, each having been multiplied by a respectiveweight. The set of weights comprises one weight for each of the images,each typically rendered at a different angle. This sum can be expressedby the following formula:

P _(combination) =w ₀ *P ₀ +w ₁ *P ₁ +w ₂ *P ₂ + . . . w _(n) *P _(n)

where w_(i) is the ith filter weight and the P_(i) are correspondingpixels, each from its own image.

In general, it is expected that the filter is normalized. That is, thesum of the set of weights should be equal to one (sometimes referred toas “unity”). It is possible, however, that some applications will useweights that sum to less than one, or greater than one, as in a specialeffect. Although this technique appears very similar to the mathematicalconstruction of alpha blending, with alpha blending, the term alpha isconceptually used to refer to the “coverage” of the pixel.

Another blending or combining technique uses logic operators. In thisblending method, values are combined by the use of a logical expression.The logical expression is applied to each bit of the value of a pixel.This has the effect that individual portions of the pixel value may beselected or masked on a per-bit basis. This particular method will haveapplications where image mattes are used. For example,

-   blended output=P₁ AND P₂; or-   blended output=P₁ AND NOT P₂

It will be appreciated that the techniques described herein forcombining the multiple rendered images are exemplary, and do not providea comprehensive recitation of all possible combining alternatives.Consequently, the particular technique for combining the multiplerendered images should not be interpreted as limiting the scope of thepresent invention, except to the extent the limitation is recited in theclaims appended hereto.

As previously described, in the embodiment of the invention illustratedin FIG. 7, a scene is rasterized at both a first and a second angle. Itshould be noted that the time at which the scene is rasterized at thefirst and second angles may be at the same instant, or at two differentinstants. That is, the “same instant” is not intended to mean that thescene is simultaneously rasterized at the two different angles, butrather, the scene has not advanced or changed from the timerasterization at the first angle occurs and when rasterization at thesecond angle occurs. Thus, rasterization at the first and second anglescapture the scene at identical moments in time.

In contrast, rasterizing at the two angles at different instants isintended to mean that the scene has changed from when the rasterizationat the first angle occurs and when the rasterization at the second angleoccurs. In this manner, a sequence of frames can be created and blendedtogether. After two initial frames are rasterized and blended, asubsequent rasterized frame can be blended with the previous, single,non-composite image, thus, two consecutive frames are blended togetherfor each output frame. As a result, when scene geometry moves at highspeeds, the motion will tend to appear smoother, while motion at lowerspeeds will yield more anti-aliasing.

Although the embodiments of the invention described with respect to FIG.7 have been described as combining only two different renderingsresulting from the rasterization of a scene at two different angles, itwill be appreciated that any plurality of renderings can be combined toform the resultant image. Combining more than two renderings may resultin a resultant image having higher visual quality; however, processingcapabilities and resources of the graphics processing system should beconsidered.

It will be further appreciated that multiple frames of texels and pixelsmay be combined using various alternative techniques to form a resultantimage and still remain within the scope of the present invention. Forexample, the embodiment shown in FIG. 7 combined the frames of pixelsfollowing the rendering of the polygon surfaces. However, the multipleframes could alternatively be combined by averaging the values ofcorresponding texels in the multiple texture maps prior to being appliedto the polygon surface. That is, the texel values of a texel applied tothe polygon is the average of the texel values for correspondinglylocated texels of the multiple texture maps.

Embodiments of the present invention have been described to this pointas separate variations of embodiments of the present invention. It willbe appreciated, however, that the various embodiments so described canbe combined to provide additional alternative embodiments of the presentinvention. For example, anti-aliased rendering according to embodimentsof the present invention can include super-sampling during the initialrasterization of the scene as well as bilinear filtering when convertingpixels to a texture map. Similarly, bilinear filtering and rasterizationat multiple angles can be combined to produce another embodiment. Thus,embodiments resulting from the combination of the embodimentsparticularly described herein remain within the scope of the presentinvention.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. For example, embodiments of thepresent invention have been described as being implemented in portionsof the pixel engine 212 (FIG. 2) and performed by using conventionalprocessing stages typically included in graphic processing systems. Theability to implement the present full-scene anti-aliased renderinginvention with conventional processing stages is an advantage which thepresent invention provides. However, it will be appreciated thatembodiments of the present invention may also be implemented incircuitry dedicated to performing full-scene anti-aliasing as describedherein. Additionally, although the present invention has been describedas being implemented in hardware embodiments, it will be appreciatedthat the present invention may also be implemented in softwareembodiments, or combinations of hardware and software. It will befurther appreciated by those of ordinary skill in the art thatembodiments of the present invention are not limited to implementationin a computer system. For example, embodiments of the present inventioncan be implemented in game machines, cellular phones, and other systemswhere rendering of anti-aliased images would be desirable. Accordingly,the invention is not limited except as by the appended claims.

1. A system for full-scene anti-aliased rendering of a scene, the systemcomprising: rasterization means for rasterizing the scene into a rasterwith a raster coordinate system rotated by a first angle relative to aviewing coordinate system; conversion means for converting pixels of theraster to texels of a texture map; application means for applying thetexture map to a surface; and rendering means for rendering a least aportion of the surface with a surface coordinate system at a secondangle relative to the viewing coordinate system, the first and secondangles being inversely related.
 2. The system of claim 1 wherein therasterizing means calculates a plurality of sample values for each pixelof the final image.
 3. The system of claim 1 wherein the first angle israndomly selected.
 4. The system of claim 1 wherein the first angle israndomly selected from a group of preselected angles.
 5. The system ofclaim 1 wherein the conversion means filters the pixels to produce thetexels of the texture map.
 6. The system of claim 1 wherein theconversion means bilinearly filters the pixels to produce the texels ofthe texture map.
 7. The system of claim 1 wherein the conversion meanstranslates each pixel into a corresponding texel on a one-to-one basis,wherein each texel is formatted for use in a texel-map.
 8. The system ofclaim 1 wherein the conversion means performs a vacuous operation,wherein the pixels are directly interpreted as texels.
 9. The system ofclaim 1 wherein the second angle is an inverse of the first angle, eachangle being measured about an axis of rotation perpendicular to aviewing plane in which the scene is rendered.